Production of tubing



Sept 19, 1967 D. ZUCKER ET-AL 3,342,648

PRODUCTION OF TUBING April 22, 1963 5 sheetg shee-t Fig. l.

WITTNESSES INVENTORS f Duvid Zucker 0nd P 19, 1967 D. ZUCKER ETAL 3,342,648

PRODUCTI ON OF TUBING Filed April 22, 1963 3 Sheets-Sheet 2 Fig. '3.

Sept. 19, 1967 D. ZUCKER ETAL PRODUCTION OF TUBING 3 Sheets-Sheet Filed April 22, 1963 Fig.4.

United States Patent 3,342,648 PRODUCTION OF TUBING David Zucker, Pittsburgh, and Robert A. Jackson, Finleyville, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 22, 1963, Ser. No. 274,549 Claims. (Cl. 148-11.5)

This invention relates to the production of tubing from metals which cannot be readily swaged or drawn or which are subject to excessive oxidation upon annealing.

As is known, metal tubing is usually produced by initially extruding or otherwise producing a relatively thick tubular blank which is subsequently either drawn through a die or swaged a number of times. In this process, the diameter and thickness of the blank is reduced and its length increased, the repeated draws or swaging operations producing a cold-working effect which improves the physical properties of the final product. In some case, the cold-working necessitates annealing of the blank between sucessive draws or swaging operations to remove excessive brittleness produced during plastic deformation.

Commercial production of tubing in this manner from certain metals and their alloys is exceedingly costly and difficult either because the metals are highly reactive and oxidize excessively during annealing or because of seizing or galling of the workpiece in being swaged or drawn through a die. That is, the workpiece, in contrast to metals such as copper and aluminum, tends to stick to the die during the drawing or swaging operation with the result that drawing is extremely difiicult and the resulting surface of the workpiece is rough and/ or sealed. The

production of tubing from ziroconium and its alloys, for example, is extremely difficult due to the tendency of the material to seize and the necessity for numerous protective anneals in a vacuum or inert atmosphere The same is true of titanium and its alloys. i

As one object, the present invention seeks to provide a method whereby tubing formed from metals subject to galling or seizing can be readily produced in large quantities.

Another object of the invention is to provide a method whereby highly reactive and oxidizable metals can be formed into tubing by drawing or swaging techniques without the necessity for costly protective anneals under vacuum or inert atmosphere conditions.

Still another object of the invention is to provide, as an article of manufacture, a workpiece from which tubing may be drawn comprising a tubular core of a highly reactive metal or a metal subject to seizing clad with a meta-l protective jacket which prevents seizing and at the same time prevents oxidation or other contamination of the workpiece during annealing.

In accordance with the invention, we produce tubing from metals which cannot be readily drawn because of seizing or which are highly reactive by the steps of initially cladding the tubular stock to be drawn with a metal which draws readily and which is not subject to excessive oxidation, thereafter drawing or otherwise plastically deforming the tubular stock with the cladding thereon to reduce the diameter of the stock while increasing its length, performing any necessary annealing in air while the cladding is in place, and finally removing the cladding. In the case where the tubing is formed in a drawing operation with the workpiece being drawn through a die and over a mandrel, both the inside and outside diameters of the highly reactive tubing or tubing subject to seizing must be clad. In the case where the tubing is formed in a swaging operation requiring a copper or the like core, the inside diameter of the tube which is highly reactive or subject to seizing need not necessarily be clad since 3,342,648 .Patented Sept. 19, 1967 the copper core itself serves to protect the inner surface. 7

However, in certain applications cladding of the inside diameter may also be necessary or desirable even in this latter case, depending upon requirements.

The above and other objects and features of the invention will become apparent from the following de tailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIGURE 1 is an illustration of one embodiment of the invention wherein the tubing is formed by a drawing process;

FIG. 1A is an illustration of a modified drawing process of this invention;

FIG. 2 is an illustration of another embodiment of the invention wherein the tubing is formed in a swaging process, and the internal diameter of the tube is not separately clad, but is prevented from exposure to air by a central core;

FIG. 3 is an illustration of an embodiment of the invention employing swaging which is similar to that of FIG. 2 except that both the internal and external diameters of the tubing are clad;

FIG. 4 is an illustration of a further embodiment of this invention for producing tubing of non-circular cross section; and

FIG. 5 is a sectional view of the apparatus illustrated FIG. 4 and taken along the lines V-V thereof. Referring now to the drawings, and particularly to FIG. 1, there is shown a tubular workpiece 10 comprising an inner core 12 of a metal such as an alloy of zirconium or an alloy of titanium which is either highly reactive so as to readily oxidize under annealing conditions or is subject to seizing or galling. The outside diameter of the core 12 is clad with a metal jacket 14; and, likewise, its inner diameter is clad with a similar protective jacket 16. In the drawing process, a reduced diameter end 18 of the workpiece is pointed to be passed through a drawing die opening to begin the drawing process. More specifically, the pointed end 18 is initially passed through an opening 20 in a die 22, and a mandrel 24 having an enlarged head 26, formed from a hardened material, such as steel, is inserted into the tube such that the enlarged head 26 will become lodged in the workpiece 10 in the area of opening 20. The trailing end of the mandrel 24 (Le, the left end as viewed in FIG. 1) is securely fixed such that the enlarged head 26 cannot move further to the right from its position shown in the drawing.

At the beginning of the drawing operation, the workpiece 10 is initially loaded onto the mandrel 24, and its swaged or reduced diameter end 18 is inserted through the die opening 20. Thereafter, the reduced diameter end 18 is securely gripped by jaws on a drawbench draw carriage, not shown, which moves to the right away from the die 22, thereby pulling the workpiece 10 through the die opening 20. In this manner, the diameter of the workpiece is reduced and its length increased.

As will be understood, pulling of the workpiece 10 through the die opening 20 produces a cold-working effeet. As was explained above, it was more or less common practice previous to the present invention to attempt to draw metals such as zirconium and titanium and their alloys Without a protective cladding. Such metals, however, are extremely difiicult to draw because of seizing or galling and require that the workpiece 10 be annealed in a non-oxidizing atmosphere or under vacuum conditions in order to prevent excessive oxidation and/or contamination during the annealing process. Since the workpiece may have to be drawn through the die a large number of times before it is reduced to its final size, and since an anneal is required between successive drawing operations, it can be readily appreciated that the production of tubing from metals such as zirconium and titanium with prior art procedures is a very costly and difficult process.

In accordance with the present invention as shown in FIGURE 1, however, the tubing 12 formed from metals such as zirconium, titanium or their alloys is clad with the protective jackets 14 and 16 before the initial drawing operation is performed. Preferably, the jackets 14 and 16 are formed from a low carbon steel; however, any metal may be used which does not seize and which will protect the inner core 12 during an annealing process, such as copper. It has been determined, however, that a low carbon steel clad performs more satisfactorily than copper, although the latter metal has been successfully used. The steel jacketing however, produces a satisfactory surface finish on all the contacting surfaces of a zirconium or zirconium alloy workpiece. Furthermore, higher annealing temperatures can be used with a steel jacket in view of the relatively high temperatures at which zirconium-iron intermetallic compounds are formed. With the procedure shown in FIG. 1, the jackets 14 and 16 act, in effect, as a lubricant for the inner core 12 during a drawing operation. After the workpiece 10 including the inner core 12 is reduced to the desired diameter, the metal cladding (i.e., jackets 14 and 16) can be readily removed by dipping the tube assembly or workpiece 10 in an acid bath, such as a 50% HNO solution. If desired, the internal jacket 16 may be removed by either pumping the acid solution through the tube or into the tube as the situation permits. For improved surface finish, it is desirable that the workpiece 10 be sandblasted or rubbed with emery cloth after each anneal to remove scale, although this is not absolutely necessary since the scale formed during the anneal is usually very loose and fiakey. It has been determined that annealing is required after each 30% of reduction of the workpiece. The annealing temperature may vary from 1300 to l550 in air. It has also been determined that the annealing time at tempera ture may vary from as short as minutes at the higher portion of the temperature range to 30 to 60 minutes at the lower end of the temperature range. However, it is to be realized that at the higher annealing times and temperatures, flaking and scaling of the jacket 14 increases in severity. Sandblasting has satisfactorily removed such scaling. It is to be realized that when an exposed inner jacket 16 is utilized, sandblasting of the interior of the workpiece is difficult and lower annealing temperatures desirably are utilized to prevent excessive scaling of the interior clad 16.

Other methods of annealing may be employed. However, a bare or unclad core 12 must be annealed in an argon atmosphere requiring that the bare reactive metal core 12 be also cooled in an argon atmosphere. In ac cordance with the prior art, a forty-five minute cooling of the workpiece 10 in argon after each anneal has been found to be necessary. It is to realized that the instant invention contemplates an anneal of the workpiece 10 in air, at a substantial time saving rather than in an inert atmosphere such as argon. If a bare or unclad core 12 were to be vacuum annealed, the cycle would be at least four hours per anneal.

The embodiment of this invention illustrated in FIG- URE 1 desirably is utilized only for larger diameter tubing lengths. It will be appreciated that for smaller diameter tubing, it is extremely difiicult to utilize a stationary mandrel 24 in view of the very small internal diameter of the workpiece.

For such small diameter tubing it has been found desirable to utilize a fixed internal mandrel such as a plug or core which is encapsulated in and extends substantially the entire length of the workpiece. An example of this arrangement is illustrated in FIG. 1A. This figure 1's similar to FIGURE 1 and like parts are designated by the same reference characters primed.

In this embodiment of the invention the relatively hard, stationary mandrel 24, of FIGURE 1 is replaced by a relatively softer deformable plug or mandrel 24', preferably formed from copper. The mandrel 24 is drawn through the opening 20 as a part of the workpiece 10 and as such is concurrently reduced in diameter and elongated by the drawing process. If desired, the workpiece 10' can be initially compacted in a swage to provide intimate contact between the adjacent surfaces of the portions 12', 14, 16' and 24 of the workpiece 10'. With the above exceptions the process of FIG. 1A is the same as that described in conjunction with FIGURE 1.

Referring now to FIG. 2, there is shown a method for producing tubing of a highly reactive metal or a metal subject to seizing by the use of a swaging process. In this case, the workpiece 28 again includes a core 30 formed from a highly reactive metal or a metal subject to seizing. The outside diameter of the core 30 is, as in the embodiment of FIGURE 1, clad with a metal protective jacket 32, desirably formed from a low carbon steel or any suitable material capable of providing a relatively smooth surface on the contacting surfaces of the core 30. The swaging process requires an internal core, and this core is provided by means of a copper plug 34, the plug 34 also acting to protect the internal diameter of the core 30 during anneals.

The swaging machine (not shown) includes two dies 36 and 38 each of which is adapted to reciprocate in the direction of arrows 40. The dies 36 and 38 are incorporated into a machine comprising a mechanical means for rapidly opening and closing the dies by reciprocating them along the path of arrows 40. The dies are carried in a slot in the face of a revolving spindle and are held between a pair of steel blocks usually called backers. Around the spindle is a circular roll cage containing a number of hardened steel rolls. Revolution of the spindle causes the backers and the dies 36 and 38- to pass between successive pairs of opposing rolls, thereby forcing the dies together along the path of arrows 40. In this manner, it can be seen that the dies 36 and 38 rotate around the workpiece 28 and are at the same time reciprocated toward and away from each other while the workpiece 28 is moved from left to right as viewed in FIG. 2.

The dies 36 and 38 are blocks of hardened steel or the like having upon their inner faces 42 and 44 the impression of the shape of the work to be produced. The left end of the die groove is flared outwardly as at 46 to allow the unreduced stock to enter.

In the swaging process, the workpiece 28 is moved from left to right as mentioned above While the dies 36 and 38 reciprocate inwardly and outwardly along the direction of arrows 40 while being rotated around the workpiece 28. In this process, the workpiece 28 is effectively hammered into a reduced cross-sectional area while its length is increased, the internal copper core 34 serving to prevent collapse of the tubing during the swaging process. Between successive swages, the workpiece 28 desirably is annealed in the same manner described in conjunction with FIGURE 1 and the resulting scale on the outer jacket 32 is preferably removed by sandblasting in the manner described above. Aftter the workpiece 28 is reduced to its final or desired diameter, both the copper core 34 and the outer jacket 32 may be removed by suitable means, such as nitric acid.

With reference now to FIG. 3, the embodiment of the invention shown is similar to that of FIG. 2; and, accordingly, elements in FIG. 3 which correspond to those shown in FIG. 2 are identified by like reference numerals. In this case, however, the internal diameter of the core 30 is clad with a protective jacket 48 as well as the outside diameter. Positioned within the inner protective jacket 48 is the copper core 34.

Considering now the embodiment of this invention illustrated in FIGS. 4 and 5, there is shown therein an apparatus for obtaining tubing of non-circular cross section with the tubing material being formed from a reactive material which readily oxidizes in air under annealing conditions or is subject to seizing or galling during the formation process. More specifically, there is illus trated in FIGS. 4 and 5 an apparatus for forming from a circular core 52, a final product comprising tubing having a generally rectangular cross section.

In accordance with the invention, a generally circular workpiece 50 includes a core 52 formed from one of the aforementioned reactive materials, such as zirconium and its alloys and titanium and its alloys. The core 52 receives therein a generally annular inner cladding member 54 desirably formed to be closely'received within the core 52 and formed from a suitable material such as copper or a low carbon steel. A tubular outer clad 56 receives therein the assembly of the core 52 and inner clad 54. The outer clad 56 desirably also is of annular configuration and is formed from a suitable material such as a low carbon steel or copper. In accordance with the invention, one of the ends of the workpiece 50 desirably is pointed to begin the drawing process for the workpiece 50. Normally, prior to drawing the tubing to its desired shape and size, the workpiece 50 is compacted in a suitable manner such as by swaging to provide intimate contact between adjacent surfaces of the core 52 and inner and outer cladding pieces 54 and 56. The workpiece 50 is then drawn through a series of rollers, assembled to provide an outer cross-sectional area of the shape desired. In this example a Turks-head roller assembly 60 is provided and includes four rollers 62 formed from a relatively hard material such as steel and fixedly positioned to provide an opening therein of the desired crosssectionalshape. Each of the rollers 62 desirably is rotatable about rigidly mounted axes 64. As is illustrated in FIG. 5, the opening 66 formed by the rollers 62 is of rectangular cross section so that when the workpiece 50 is drawn therethrough, the rollers act to collapse the protruding sides of the workpiece 50 to form a final member of rectangular cross section. Each of the rollers 62 desirably is adjustably mounted on a suitable frame (not shown) to permit variations of the size of the opening66 during the drawing procedure. The workpiece 50 desirably is drawn to the rollers in the direction indicated by the arrows 68.

It willbe appreciated that for the formation of tubing wherein large reductions in size are not necessary, an annular inner clad or core 54 is substituted for the solid cores 34 illustrated in FIGS. 2 and 3. After each pass of the workpiece through the opening 66, the rollers 62 are adjusted to decrease the size of the opening 66 for subsequent passes in order to form the workpiece 50 to its desired final size.

As described in conjunction with other embodiments of this invention, the workpiece 50 desirably is annealed in the same manner heretofore described, i.e., at least after each 30% of reduction of the sides thereof.

There now follows specific examples of the formation of tubing employing certain of the processes heretofore described and combinations thereof:

EXAMPLE I of zirconium and initially comprised a length of tubing having an outer diameter of 0.420 inch. The inner cladding member 16' initially comprised a low carbon steel tube having an outer diameter of 0.318 inch. The mandrel or plug 24' comprised a copper rod having a diameter of 0.215 inch. The workpiece was initially swaged in suitable apparatus such as the dies 36 and 38 illustrated in. FIGS. 2 and 3 for the purpose of compacting the TABLE I.-SWAGING FOR COMPACTION OF ASSEMBLY Swage Die Anneal Workpiece Outer Opening, Inches Diameter, Inches Indicates annealing 10 min. in air at 1,450" F.

After the assembly was compacted, the workpiece 10 was passed through a suitable drawing die such as the 22 of FIG. 1A having an opening 20' therein. After each pass, the size of the die opening 20' was varied and the workpiece 10' was repointed at 18 pursuant to the following Table II. An annealing step was utilized after each approximately 30% reduction with the annealing taking place in air at 1450 F. for 10 minutes. The annealed assembly was sandblasted prior to the next drawing pass. The final size of the core 12, after the inner and outer cladding had ben removed by a 50% solution of nitric acid, was 0.094 inch outer diameter.

TABLE IL-DRAWING PASS SCHEDULE Die Opening, Outer Diameter Outer Diameter Inches of Workpiece, of Pointed End, Anneal riches Inches Indicates annealing step at pass completion.

EXAMPLE II The following example employs a process of FIG. 3 wherein a 0.420 inch outer diameter zirconium alloy tubing-lengthwas swaged. More specifically, the outer cladding piece 32 comprised a low carbon steel tube having a 0.502 inch outer diameter and the inner core 48 comprised a low carbon steel tube having an outer diameter of 0.318 inch. The core 34 comprised a copper rod having an outer diameter of 0.215 inch. The workpiece 28, as described above, was reduced in a swage with approximately 30% reductions per pass and with an air anneal at 1450 F. for 15 minutes after each pass. After each anneal, the assembly was sandblasted. The sandblasting operation took 10 minutes for the workpiece.

The swaging pass schedule for Example II is described in Table III.

TABLE III.--PASS SCHEDULE FOR SWAGING OF EXAMPLE II Swaged die Outer diameter of opening, inches: workpiece, inches .440 .465 .408 .409 .340 .350 304 30V 256 .261 215 .218 180 .183 152 .155 125 .129 115 .115

The following example is similar to Example II and illustrates the swaging process of FIG. 3. In this example a workpiece of the same dimensions as utilized in Example II Was constructed. The workpiece was reduced in swage with approximately 30% reductions per pass and with an air anneal at 1400" F. for 10 minutes after each 30% reduction. The annealed assembly was sandblasted prior to further reductions with the sandblasting operation taking approximately 10 minutes. At certain stages of the swaging operation, a portion of the outer cladding was removed and the outer diameter of the zirconium alloy tube was measured. The annealing schedule is indicated by an asterisk in the appropriate column in the following Table IV which shows the pass schedule for Example III.

TABLE IV.-SWAGIN G OPERATION PASS SCHEDULE Outer Workpiece Diameter Swage Die Outer Reduction of Zirconium Opening Diameter, (Percent- Anneals" Alloy Tube,

Inches Inches age) Inches EXAMPLE IV This example is illustrative of the process for forming a zirconium alloy tubing member of generally rectangular cross section pursuant to the embodiment of this invention illustrated in FIGS. 4 and 5. The starting materials comprise an outer cladding member 56 formed from a low carbon steel tube having a 0.410 inch outer diameter, a length of zirconium alloy tubing 52 having a 0.320 inch outer diameter and an inner cladding tube 54 of copper having a 19, inch wall and having a 0.250 inch outer diameter. The above-described assembly was reduced in a swage having a die opening of 0.375 inch for the purpose of compacting the assembly. The outer diameter of the workpiece after the swaging pass was measured to be 0.387 inch. A Turks-head roller assembly having a final overall opening of rectangular cross section with the size thereof being 0.370 inch and 0.148 inch, respectively, was utilized in the drawing operation prior toremoving the outer clad member. After the eighth pass through the Turks-head rollers, the outer cladding was removed by a 50% nitric acid solution and the cross section of the exposed assembly was reduced to its final desired size of 0.305 inch by 0.080 inch. After each of the first seven passes through the Turks-head assembly, an air anneal of the workpiece was performed at 1450 F. for 10 minutes. The inner copper core was removed after the final sizing. The following Table V is illustrative of the pass schedule for the Turks-head drawing operation. The Turks-head roller assembly comprised two rollers disposed vertically and two rollers disposed horizontally. In considering Table V, the roller setting for the vertical rollers and for the horizontal rollers will be depicted separately. One of the ends of the workpiece was pointed by a suitable swaging operation prior to each of the jacketed passes.

TABLE V Pointed Vertical Workpieee Horizontal Horizontal End Outer Rollers, Vertical Rollers Dimension, Diameter, Setting, Dimension, Setting, Inches Inches Inches Inches Inches 1 Measurements discontinued.

EXAMPLE V This example is illustrative of the process for forming small diameter tubing from reactive tubular stock pursuant to the embodiment of this invention described in conjunction with FIG. 2.

The starting materials for forming the workpiece 28 of FIG. 2 comprised a copper core 34 made from a 0.320 inch outer diameter copper rod, a core 30' of zirconium alloy tubing having an initial outer diameter of 0.420 inch which received the copper rod 34 therein, and an outer tubular clad member 32 which receives the assembled core 30 and rod 34 therein. The outer clad member 32 comprised a 0.500 inch outer diameter low carbon steel tube.

The workpiece 28 was reduced in swage dies 38 and 36 with approximately 30% reductions per pass. An air anneal to the workpiece 28 was performed for 15 minutes at 1550 F. following each pass. Following each anneal, the workpice was sandblasted for 10 minutes to remove scale from the outer clad 32. The outer cladding was removed prior to the last pass. A zirconium alloy tube was produced pursuant to this example having a final outer diameter of 0.119 inch. The pass schedule for this example is shown in Table VI.

TABLE VI.PASS SCHEDULE FOR OUTER GLAD SWAGED TUBING Referring to Table VI, at the end of the eighth pass, the exterior steel tube was removed from the workpiece. Measurements subsequent to the eighth pass were .made on the exposed zirconium alloy tubing. No annealing took place subsequent to the eighth pass.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention. For example, the removal of the inner cladding 16 of FIG. 1A so that the outer surface of the mandrel 24 serves also as an inner cladding is within the contemplation of this invention. Accordingly, it is specifically intended that the afore-described specific embodiments and examples be interpreted as illustrative, rather than in a limiting sense.

We claim as our invention:

1. A method for producing relatively smaller tubing from reactive metals which cannot be readily plastically deformed selected from the group consisting of zirconium and titanium and alloys thereof, respectively, comprising the steps of cladding both the inside and outside surfaces of relatively larger tubular stock of said reactive metal with members formed from a metal which can be readily plastically deformed, cold working the clad assembly to produce intimate contact between said tubular stock and said members, reducing the diameter of the clad assembly while increasing its length, and thereafter removing said claddings.

2. The method of claim 1 including the step of an nealing the clad assembly in air after a predetermined reduction of the diameter thereof.

3. The method of claim 2 wherein the predetermined reduction of the diameter is approximately a 30% reduction.

4. The method of claim 1 wherein the clad assembly is swaged to provide the intimate contact between the tubular stock and said members.

5. The method of claim 2 wherein the clad assembly is annealed in air at a temperature of from 1300 to 1550 F. for from 5 to 60 minutes.

6. The method of claim 2 wherein the exterior of clad assembly is cleaned after annealing to remove scale therefrom and wherein the steps of reducing the diameter of the clad assembly and annealing are repeated after cleaning until a predetermined final diameter thereof is ob tained.

7. In a method of producing relatively smaller diameter tubing from relatively larger diameter tubular stock selected from the group consisting of zirconium and its alloys and titanium and its alloys, the steps comprising cladding the interior and exterior of said stock with a clad material selected from the group consisting of iron and its alloys and copper to form a workpiece, elongating said workpiece thereby reducing the outer diameter thereof, annealing said workpiece in air after at least each 30% of reduction in the outer diameter thereof, and removing said clad material after said tubular stock has been sized to said relatively smaller diameter.

8. In a method of producing relatively smaller diameter tubing from relatively larger diameter tubular stock selected from the group consisting of zirconium and its alloys and titanium and its alloys, the steps comprising cladding the interior and exterior of said stock with a clad material selected from the group consisting of iron and its alloys and copper to form a workpiece, elongating said workpiece thereby reducing the outer diameter thereof, annealing said workpiece in air after at least each 30% of reduction in the outer diameter thereof, said annealing step being performed at a temperature between 1300 and 1550 F. for a time of from 5 to minutes, said annealing time being dependent upon the annealing temperature, and removing said clad material after said tubular stock has been sized to said relatively smaller diameter.

9. In a method of producing relatively smaller sized tubing of a predetermined cross-sectional configuration from a relatively larger sized tubular stock selected from the group consisting of zirconium and its alloys and titanium and its alloys, the steps comprising cladding the interior and exterior surfaces of said tubular stock with tubular clad members selected from the group consisting of iron and its alloys and copper to form a workpiece, passing said workpiece through an opening of the desired cross-sectional configuration, annealing said workpiece in air after passing said workpiece through said opening at least once, said annealing step being performed at a temperature between 1300 and 1550 F, for a time of from 5 to 60 minutes, said annealing time being dependent upon the annealing temperature, and removing said clad material.

10. In a method of producing relatively smaller sized tubing of a predetermined cross-sectional configuration from a relatively larger sized tubular stock selected from the group consisting of zirconium and its alloys and titanium and its alloys, the steps comprising cladding the interior and exterior surfaces of said tubular stock with tubular clad members selected from the group consisting of iron and its alloys and copper to form a workpiece, swaging said workpiece to cause intimate contact of adjacent surfaces of said stock and said tubular clad members, passing said workpiece through an opening of the desired cross-sectional configuration, annealing said workpiece in air after passing said workpiece through said opening at least once, said annealing step being performed at a temperature between 1300 and 1550 F. for a time from 5 to 60 minutes, said annealing time being dependent upon the annealing temperature, and removing said clad material.

References Cited UNITED STATES PATENTS 2,549,249 4/1951 Seabury et a1. 29 423 2,837,817 6/1958 Kelley 148-4 X 2,938,841 5/1960 Dale 29-528 X 3,075,637 1/1963 Bean et al. 72 274 X HYLAND BIZOT, Primary Examiner. DAVID L. RECK, CARL D. QUARFORTH, Examiners. H. F. SAITO, Assistant Examiner. 

10. IN A METHOD OF PRODUCING RELATIVELY SMALLER SIZED TUBING OF A PREDETERMINED CROSS-SECTIONAL CONFIGURATION FROM A RELATIVELY LARGER SIZED TUBULAR STOCK SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM AND ITS ALLOYS AND TITANIUM AND ITS ALLOYS, THE STEPS COMPRISING CLADDING THE INTERIOR AND EXTERIOR SURFACES OF SAID TUBULAR STOCK WITH TUBULAR CLAD MEMBERS SELECTED FROM THE GROUP CONSISTING OF IRON AND ITS ALLOYS AND COPPER TO FORM A WORKPIECE, SWAGING SAID WORKPIECE TO CAUSE INTIMATE CONTACT OF ADJACENT SURFACE OF SAID STOCK AND SAID TUBULAR CLAD MEMBERS, PASSING SAID WORKPIECE THROUGH AN OPENING OF THE DESIRED CROSS-SECTIONAL CONFIGURATION, ANNEALING SAID WORKPIECE IN AIR AFTER PASSING SAID WORKPIECE THROUGH SAID OPENING AT LEAST ONCE, SAID ANNEALING STEP BEING PERFORMED AT A TEMPERATURE BETWEEN 1300 AND 1550*F. FOR A TIME FROM 5 TO 60 MINUTES, SAID ANNEALING TIME BEING DEPENDENT UPON THE ANNEALING TEMPERATURE, AND REMOVING SAID CLAD MATERIAL. 